• A palette knife is the usual tool for scraping back.red image by Pefkos from Fotolia.com
  
  Scraping back is a method artists use to partially reveal the underlying layer of a canvas, which may be white, colored or a strategically placed image. With a palette knife or other implement the artist scrapes across the wet paint so that most of the color is removed. New York artist and author of "The Oil Painting Book", Bill Creevy says "What's scraped away is as revealing as what is applied; both are telling and beautiful." Reasons for scraping back vary from artist to artist.
  
  

Harmony

• Often if a painting is completely scraped back, leaving just a thin film or veil, the remaining color will pull the painting together. It can serve as an imprimatura, or early coating. Small areas of this film will show through the final painting and give it a unified look.
  
  

Color

• The colors can blend and change dramatically, sometimes in an unexpected fashion. One might see color combinations that would not be discovered otherwise.
  
  

Smudging

• Heavy lines can be softened by scraping back. It is possible then to re-draw the subject. The effect is similar to smudging charcoal lines in a drawing.
  
  

Mystery

• Writing about contemporary artist Alex Powers, Carole Katchen says "Powers considers the lost-and-found aspects of the face in shadow to be the most successful element in his work. He likes to draw unusual-looking models; his least favorite subjects are attractive women." This idea, of course, lends itself to the use of scraping back. In one of his paintings, "Nude with Face in Shadow," the model's face is nearly hidden and makes her look mysterious.
  
  

Variety

• The Impressionist Edgar Degas was a proponent of scraping back. According to writer Bernard Dunstan, "Degas' 'Elena' shows the effect clearly. Scraping has left areas in the flesh quite smooth, while others are pitted with the canvas grain....Although on the whole thinly painted, this small canvas is full of the most subtle variety of surface and brushwork." Degas was a tireless experimenter, according to Dunstan. "There are some canvases in which he even used his fingers or thumb to dab the color onto the canvas, achieving a peculiarly unaccented, 'muffled' quality.
  
  

Texture

• The surface threads of the canvas are lightened by scraping back while the hollows are still filled with paint. Linen and canvas have their own charm, and if they show through occasionally, it can add to the effect. Writing about Georgia O'Keeffe, Jane Jones says "O'Keeffe occasionally allowed the weave of the canvas to show through the paint. This gave her work added sparkle, especially in the light areas.
  
  Going back to the 18th century, Thomas Gainsborough was an artist who often used scraping back in his paintings. In a portrait of Margaret Gainsborough, for instance, a delicate transition in the cheek area is made by scraping back to the canvas.